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Abstract. The International Submillimetre Airborne Radiometer (ISMAR) has been developed as an airborne demonstrator for the Ice Cloud Imager (ICI) that will be launched on board the next generation of European polar-orbiting weather satellites in the 2020s. It currently has 15 channels at frequencies between 118 and 664 GHz which are sensitive to scattering by cloud ice, and additional channels at 874 GHz are being developed. This paper presents an overview of ISMAR and describes the algorithms used for calibration. The main sources of bias in the measurements are evaluated, as well as the radiometric sensitivity in different measurement scenarios. It is shown that for downward views from high altitude, representative of a satellite viewing geometry, the bias in most channels is less than ±1 K and the NEΔT is less than 2 K, with many channels having an NEΔT less than 1 K. In-flight calibration accuracy is also evaluated by comparison of high-altitude zenith views with radiative-transfer simulations.

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Abstract. The MARSCHALS (Millimetre-wave Airborne Receiver for Spectroscopic CHaracterisation of Atmospheric Limb-Sounding) project has the general objectives of demonstrating the measurement capabilities of a limb viewing instrument working in the millimetre and sub-millimetre spectral regions (from 294 to 349 GHz) for the study of the Upper Troposphere – Lower Stratosphere (UTLS). MARSCHALS has flown on board the M-55 stratospheric aircraft (Geophysica) in two measurements campaigns. Here we report the results of the analysis of MARSCHALS measurements during the SCOUT-O3 campaign held in Darwin (Australia) in December 2005 obtained with MARC (Millimetre-wave Atmospheric-Retrieval Code). MARSCHALS measured vertical distributions of temperature, water vapour, ozone and nitric acid in the altitude range from 10 to 20 km in presence of clouds that obscure measurements in the middle infrared spectroscopic region. The minimum altitude at which the retrieval has been possible is determined by the high water concentration typical of the tropical region rather than the extensive cloud coverage experienced during the flight. Water has been measured from 10 km to flight altitude (~18 km) with a 10% accuracy, ozone from 14 km to flight altitude with accuracy ranging from 10% to 60%, while the retrieval of nitric acid has been possible with an accuracy not better than 40% only from 16 km to flight altitude due to the low signal to noise ratio of its emission in the analysed spectral region. The results have been validated using measurement made in a less cloudy region by MIPAS-STR, an infrared limb-viewing instrument on board the M-55, during the same flight.

Terahertz-frequency quantum cascade lasers (THz QCLs) have numerous potential applications as 1-5 THz radiation sources in space science, biomedical and industrial sensing scenarios. However, the key obstacles to their wide-scale adoption outside laboratory environments have included their poor far-field beam quality and the lack of mechanically robust schemes that allow integration of QCLs with THz waveguides, mixers and other system components. A block integration scheme is presented, in which a continuous-wave ∼3.4 THz double-metal QCL is bonded into a precision-machined rectangular waveguide within a copper heat-sink block. This highly reproducible approach provides a single-lobed far-field beam profile with a divergence of ≲20°, and with no significant degradation in threshold current or in the range of operating temperatures.Introduction: Terahertz-frequency quantum cascade lasers (THz QCLs) [1] are compact sources of coherent radiation in the 1-5 THz band, with peak output powers of up to 1 W [2]. Numerous potential applications exist, including their use as local oscillators for satellite-borne astronomy and atmospheric science instrumentation [3] and as radiation sources for industrial inspection, security and biomedical imaging [4]. However, widespread commercialisation of THz QCLs has not yet been realised. One significant issue is the lack of a mechanically robust and reproducible scheme for integrating THz QCLs with external waveguides and mixers. This typically leads to large and fragile arrangements of discrete optical components, although several elegant yet complex semiconductor integration techniques have been proposed (e.g. [5]). QCLs in double-metal waveguides yield the best thermal performance, and are well-suited to 'near-field' radiation coupling (e.g. into external waveguides). However, their poor 'far-field' beam quality and wide divergence [6] lead to poor coupling into external freespace optical components. Previous beam optimisation techniques have been employed in either device patterning approaches [7,8] or assemblies of antennas or lenses [9, 10]. Although a far-field beam divergence of &20 W is achievable with these techniques, they are relatively complex and their reproducibility and mechanical robustness have not been demonstrated.We report a new packaging and waveguide-integration scheme, in which a 3.4 THz double-metal QCL is ribbon bonded to a direct current (dc) stripline within a copper (Cu) heat-sink enclosure containing a rectangular cross-section metallic waveguide. This approach makes use of highly reproducible mechanical microfabrication techniques previously developed to support the construction of waveguide-integrated THz-frequency mixers. Since the QCL cavity itself is not modified, this approach has a very low impact on the threshold current and operating temperature range of the device, while yielding a beam divergence of <20°, comparable to the previous techniques discussed above.